Off hand, it may be difficult to dig out such statistics, but I may provide you with an abstract from a study on
alcohol violations by airline pilots. As per this study, "During the study period, newspapers reported on a total of 13 incidents of alcohol violations involving 17 pilots. All but two of the incidents occurred during January 2002 through June 2006. The majority (85%) of the incidents were first identified by airport personnel, such as security screeners, based on suspicion of alcohol use by the pilot. Subsequent alcohol testing revealed a mean BAC of 90 mg/dL (ranging from 10 mg · dL−1 to 182 mg · dL−1). Of the 17 pilots, 6 were known to be prosecuted criminally, including 5 who were sentenced to jail terms."
So the majority of reports come from security screeners and other airport personnel.
